Feeling stressed? Working long hours? Desperate to do your job better? Never mind, it could mean you are in line for promotion.

Stressed teachers are more likely to be effective at work than their laidback colleagues, new research has found. They are also more motivated, and therefore more likely to be promoted at work.

Tamjid Mujtaba, of the Institute of Education in London, studied the effects of stress on more than 1,100 teachers.

She found that those teachers who work longer hours are most likely to be stressed, and secondary teachers are more prone than those at primary school. But, she suggests, extreme stress could have a positive effect on their careers.

"It is likely that teachers who are engaged in their work have high self- belief, and are motivated to achieve and strive to do better, which will inevitably lead to high stress levels," said Dr Mujtaba. "These fuel the desire to take on more demanding tasks."

Her research shows that teachers who have high levels of stress are more likely to be very effective than their more relaxed colleagues.

Only a very small number of highly effective teachers do not suffer from extreme stress: lack of anxiety usually has an adverse effect on classroom skills.

Often, motivation acts as a counterbalance to stress, so that teachers who are very motivated are able to overcome the negative effects through enthusiasm alone. The link between stress, motivation and effectiveness in class means that stressed teachers are more likely to progress in their careers. This success then leads to greater stress and, potentially, further progression.

"Striving to do better at their jobs is probably fuelled by stress, leading teachers to take on more demanding positions and increasing stress levels," said Dr Mujtaba.

But Patrick Nash, chief executive of the Teacher Support Network, said: "There's a fundamental difference between pressure and stress. A degree of pressure can be beneficial, but the physical, mental and emotional symptoms of stress are always damaging. They can have a highly destabilising effect on teachers' work and wellbeing."

Christine Blower, acting general secretary of the NUT, agrees. "Some people can work well under pressure, but no one works well under stress," she said.

"Stress, as many teachers know to their cost, can induce both mental and physical health problems."

Despite her findings, Dr Mujtaba recommends teachers should be given support in dealing with the demands and pressures of the job.

"Training courses can help teachers to develop more effective coping strategies," she said.